Effects of Ca addition on microstructure, electrochemical behavior and magnesium-air battery performance of Mg-2Zn-xCa alloys

Abstract

• Effect of Ca on the properties of second phases in Mg-Zn-Ca alloys was studied. • The optimal alloy exhibits beneficial corrosion resistance and discharge properties. • Discharge sequence of precipitated second phases was investigated. In this research, the micro-morphologies, electrochemical behaviors and battery discharge performances of the Mg-2Zn- x Ca alloys as potential anode materials were investigated. The micro-morphology results showed that for the alloy with low Ca content ( x = 0.1 and 0.2), only the Ca 2 Mg 6 Zn 3 phase was observed to precipitate in a punctate form within the crystal. As the Ca content rose, the amount of the punctate Ca 2 Mg 6 Zn 3 increased while the strip-shaped Ca 2 Mg 6 Zn 3 phase precipitated at the grain boundary was also observed. When the Ca content reached 0.5 wt% and higher, the second phases were observed to be both Mg 2 Ca and Ca 2 Mg 6 Zn 3 phase which precipitated at the grain boundary and the morphology of second phases gradually changes into a continuous network. Among the four tested alloys, the Mg-2Zn-0.2Ca sample delivered the best electrochemical activity with more negative corrosion potential and larger corrosion resistance in electrochemical experiments. Battery performance tests showed that the Mg-2Zn-0.2Ca anode exhibited an improved specific capacity of 1344.1 mAh g −1 and high anodic efficiency of 61.0% at 10 mA cm −2 . The discharge order of the precipitated phase has been derived as follows: Mg 2 Ca > Mg > Ca 2 Mg 6 Zn 3 .